Active matrix substrate, electro-optical device, and electronic device

ABSTRACT

An active matrix substrate is provided which does not cause reductions in the brightness of electroluminescence elements, and which comprises appropriate peripheral circuitry occupying a small area. The active matrix substrate comprises peripheral circuits to supply current to EL elements provided for each pixel, and corresponding to EL elements, and further comprises a holding element (C) which holds a control voltage, a first active element (T 1 ) connected to the holding element (C) and which supplies current to a light-emitting portion (OLED) based on a control voltage, and a second active element (T 2 ) connected to the holding element (C) and which controls the charging and discharging of the holding element. In particular, the second active element (T 2 ) is configured as a multiple-control-terminal type active element. As a result, there are no fluctuations in the programmed current.

This is a Divisional of application Ser. No. 10/299,861 filed Nov. 20,2002. The entire disclosure of the prior application is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an active matrix substrate suitable forelectro-optical devices, an electro-optical device, and electronicdevice.

2. Description of the Related Art

The active matrix driving method is one method of drivingelectro-optical devices comprising liquid crystal elements, organicelectroluminescence (EL) elements, electrophoretic elements, electronicemission elements, and similar. In an electro-optical device driven bythe active matrix driving method, a plurality of pixels are arranged ina matrix on the display panel. Each of the plurality of pixels comprisesa pixel circuit, in turn comprising an electro-optical element and adriving transistor which supplies driving power to the electro-opticalelement. Each of the plurality of pixel circuits is arranged tocorrespond to the intersection of a data line and a scan line (see, forexample, patent reference 1: Internationally disclosed pamphlet no.WO98/36407).

In order to precisely control brightness in an electro-optical device,the amount of power supplied to electro-optical elements must beprecisely controlled. In particular, because organic EL elements arecurrent-driving type electro-optical elements, the brightness isdirectly affected by the current. Hence there is a need to preciselysupply the desired current to organic EL elements; and in addition tooptimizing the driving circuit and driving method, the pixel layout mustalso be optimized. Problems encountered in actual pixel layouts include,for example, contact between pixel electrodes and peripheral circuitry,stability of holding capacitances, and transistor turn-off currents.

The present invention was devised in light of the above circumstances,and has as an object the provision of an active matrix substrate,electro-optical device, and electronic device comprising an optimalpixel layout for the stable driving of electro-optical elements.

SUMMARY OF THE INVENTION

In order to resolve the above problems, a first active matrix substrateof this invention is an active matrix substrate comprising peripheralcircuitry to supply a current to electro-optical elements provided ineach pixel according to the electro-optical element; each peripheralcircuit comprises a holding element to hold a control voltage, a firstactive element, connected to the holding element, to supply a current tothe electro-optical element based on the control voltage, and a secondactive element, connected to the holding element, to control thecharging and discharging of the holding element; and the above secondactive element has a structure which prevents leakage currents duringshutoff.

Here “electro-optical element” refers to general elements which emitlight, or change a status of light in response to external light, due toelectrical action, and comprises both elements which themselves emitlight, and elements which control the transmission of external light.For example, electro-optical elements include liquid crystal elements,electrophoretic elements, EL elements, and electron emission elementswhich emit light by causing electrons generated through application ofan electric field to strike an emission plate.

“Peripheral circuits” refers to the aggregation of circuit elementswhich drive each pixel in an active-matrix type electro-optical device,and comprises, for example, TFTs (thin film transistors) or similar.

“Active matrix substrate” refers to general substrates on which ismounted peripheral circuitry, regardless of whether electro-opticalelements are formed or not.

There is no particular restriction on “active elements”, which mayinclude, for example, TFTs and other transistors and diodes, or similar.

Here “holding element” refers to, for example, capacitors, memory, andother elements which hold electrical signals.

Normally, when an active element is in the non-conducting state, whereasideally there should be no current flowing, a current, albeit slight,may flow; an active element having a “structure to prevent leakagecurrents during shutoff” refers to an active element configured with theobject of preventing the occurrence of such a current (leakage current).

An example of such an element is a multi-gate type active element. Amulti-gate type active element is an active element which functions as asingle element, but strictly speaking comprises a plurality of activeelements connected in series, configured to function similarly to adevice with control terminals connected together.

In configuring a multi-gate type active element, the semiconductor layermay be in a curved shape, as in an embodiment described below, or thegate shape may be curved.

The second active element may be a transistor with a structure selectedfrom the group consisting of an LDD structure, GDD structure, or DDDstructure. Here “LDD” is an abbreviation of “Lightly Doped Drain”; “GDD”is an abbreviation of “Graded Diffused Drain”; and “DDD” is anabbreviation of “Double Diffused Drain”. In a transistor having thesestructures, in order to limit the adverse effects of hot electrons andsimilar during fine MOSFET fabrication, the maximum electric field nearthe drain is weakened. For example, in such transistors the drain regionof the transistor is lightly doped with impurities to relax the electricfield in regions where impurity diffusion is performed and betweensilicon substrates; for example, n-type regions may be formed usingself-alignment.

In such transistors, because the source-drain resistance while thetransistor is turned off is extremely high and leakage currents arereduced, electric charge accumulated in the holding element is notreleased, and the electric potential applied to a control terminal canbe maintained at a constant level.

A second active matrix substrate of this invention is an active matrixsubstrate comprising a plurality of unit circuits, arranged tocorrespond to the intersections of a plurality of data lines and aplurality of scan lines. Each of the above plurality of unit circuitscomprises a first transistor, which comprises a first control terminal,first terminal, and second terminal; a holding element, connected to theabove first control terminal, comprising a first electrode and a secondelectrode; and a second transistor, comprising a third terminal, afourth terminal, and a second control terminal, wherein the above thirdterminal and the above fourth terminal are respectively connected to theabove first terminal and to the above first electrode; and the abovesecond transistor has a multi-gate structure.

In the above active matrix substrate, in place of a multi-gatestructure, the above second transistor may be a transistor with astructure selected from an LDD structure, GDD structure, or DDDstructure.

By adopting a multi-gate structure and an LDD structure, GDD structure,or DDD structure, the leakage current when the second transistor is inthe turned-off state can be reduced, so that the electric chargeaccumulated in the holding element can be maintained for a long periodof time.

In the above active matrix substrate, it is preferable that the abovefirst transistor and the above second transistor have differentconduction types. In this case, it is preferable that the semiconductorfilm constituting the above first transistor and the semiconductor filmconstituting the above second transistor be separated.

For example, it is preferable that the above first transistor by p-type,and that the above second transistor be n-type.

The above active matrix substrate may further comprise a thirdtransistor, comprising a fifth terminal, a sixth terminal, and a thirdcontrol terminal, with the above third control terminal connected to onescan line among the above plurality of scan lines, and the above fifthterminal connected to one data line among the above plurality of datalines.

The above sixth terminal may be connected to the above third terminaland to the above first terminal.

In the above active matrix substrate, the above active matrix substratemay have a stacked-layer structure comprising a plurality of layers; theabove plurality of layers may comprise a semiconductor layer, in whichis formed a semiconductor film constituting the above first and secondtransistors, and a gate metal layer, in which are formed the abovesecond control terminals; and in the above gate metal layer there may beformed at least one portion of at least one scan line among the aboveplurality of scan lines.

By this means, the above second control terminal and at least oneportion of the scan line can be formed in the same process, so thatmanufacturing processes can be shortened.

In the above active matrix substrate, the above active matrix substratemay have a stacked-layer structure comprising a plurality of layers; theabove plurality of layers may comprise a semiconductor layer, in whichis formed a semiconductor film constituting the above first and secondtransistors, and a gate metal layer, in which are formed the abovesecond control terminals; and in the above gate metal layer there may beformed at least one portion of at least one data line among the aboveplurality of data lines.

By this means, the above second control terminal and at least oneportion of the data line can be formed in the same process, so thatmanufacturing processes can be shortened.

In the above active matrix substrate, the above active matrix substratemay have a stacked-layer structure comprising a plurality of layers; theabove plurality of layers may comprise a semiconductor layer, in whichis formed a semiconductor film constituting the above first and secondtransistors, a gate metal layer, in which are formed the above secondcontrol terminals, and a source metal layer, in which is formed a sourceelectrode or drain electrode connected to the source or to the drain ofthe above second transistor; and at least one portion of at least onedata line among the above plurality of data lines may be formed in thelayer closer to the above semiconductor layer among the above sourcemetal layer and the above gate metal layer.

By this means, when an electro-optical device is formed in whichelectro-optical elements are arranged above the active matrix substrate,at least one portion of a data line can be separated from the electrodesof electro-optical elements, so that operation delays due to straycapacitances occurring between electrodes and data lines can be reduced.

A third active matrix substrate of this invention comprises unitcircuits, comprising transistors, as well as data lines and scan lines,and has a stacked-layer structure comprising a plurality of layers; theabove plurality of layers comprises a semiconductor layer, in which isformed a semiconductor film constituting transistors, and a gate metallayer, in which are formed the gate terminals of the above transistors;and at lease one portion of either the above scan lines, or the abovedata lines, or both, is formed in the above gate metal layer.

By this means, transistor gate terminals and at least one portion of thescan lines or data lines can be manufactured by the same process, sothat manufacturing processes can be shortened.

A fourth active matrix substrate of this invention comprises unitcircuits, comprising transistors, as well as data lines and scan lines,and has a stacked-layer structure comprising a plurality of layers; theabove plurality of layers comprises a semiconductor layer, in which isformed a semiconductor film constituting transistors, a gate metallayer, in which are formed the gate terminals of the above transistors,and a source metal layer in which are formed the source electrodes ordrain electrodes which are connected to the sources or drains of theabove transistors; and at lease one portion of either the above scanlines, or the above data lines, or both, is formed in the layer, amongthe above gate metal layer and the above source metal layer, which iscloser to the above semiconductor layer.

In the above active matrix substrate, when an electro-optical device isformed in which electro-optical elements are arranged above the activematrix substrate, at least one portion of data lines or scan lines canbe separated from the electrodes of electro-optical elements, so thatdelays in signal supply due to stray capacitances occurring betweenelectrodes and data lines or scan lines can be suppressed.

In the above active matrix substrate, it is preferable that a unitcircuit comprise a first transistor, comprising a first controlterminal, a first terminal, and a second terminal; a holding element,connected to the above first control terminal, and comprising a firstelectrode and a second electrode; and a second transistor, comprising athird terminal, a fourth terminal, and a second control terminal,wherein the above third terminal and the above fourth terminal arerespectively connected to the above first terminal and to the abovefirst electrode; and that the unit circuit have at least a structureselected from an LDD structure, GDD structure, DDD structure, ormulti-gate structure.

The LDD structure, GDD structure, DDD structure, and multi-gatestructure are appropriate structures for suppressing current leaks, andso by employing such a configuration, the electric charge accumulated inthe holding element can be maintained for long periods of time.

A first electro-optical device of this invention comprises the aboveactive matrix substrate, and electro-optical elements.

A second electro-optical device of this invention comprises peripheralcircuits to supply current to electro-optical elements provided for eachpixel, corresponding to the above electro-optical elements; each of theabove peripheral circuits comprises a light emission-controlling activeelement to supply current to the above electro-optical element duringthe light emission period, a holding element to hold a control voltage,a first active element the gate terminal of which is connected to theabove holding element and which supplies a current based on the abovecontrol voltage applied to the gate terminal to the aboveelectro-optical element, via the above light emission-controlling activeelement, a current-controlling active element which passes a constantcurrent (or a data current) via the above first active element duringthe selection period, and a second active element connected between theabove current-controlling active element and the above holding element,which charges the above holding element during the above selectionperiod and which stores the above control voltage; and the above secondactive element comprises a structure to prevent leakage currents duringshutoff.

As the above structure to prevent leakage currents, similarly to thecase of the above active matrix substrates, for example, an LDDstructure, GDD structure, DDD structure, or multi-gate structure can beadopted.

In the above electro-optical device, as the above first active elementand the above second active element, it is preferable that, for example,a transistor be used. In this case, it is preferable that thetransistors have different conduction types. For example, it ispreferable that the above first active element be p-type, and that theabove second active element be n-type.

Corresponding to this, a configuration may be adopted comprising a firstdriver circuit which supplies negative-logic data signals to the firstactive element, and a second driver circuit which suppliespositive-logic scan signals to the second active element.

In the above electro-optical device, a configuration may be adoptedcomprising data lines which supply data signals to first activeelements, and scan lines, intersecting the data lines, which supply scansignals to second active elements.

In the above electro-optical device, it is preferable that either thedata lines or the scan lines be wired by means of the metal layer, amongthe source metal layer and the gate metal layer which comprise the firstactive elements and second active elements, which is separated from thecommon electrodes of the electro-optical elements. This is because ifthe metal layer which is more distant from the common electrodes isused, the stray capacitance arising between the signal lines and thecommon electrodes can be reduced.

Specifically, the scan lines may for example be wired using the gatemetal layer which forms the gate terminals of the second activeelements.

In the above electro-optical device, it is preferable that, among theplurality of active elements, the plurality of active elements havingthe same polarity be formed continuously and in planar fashion in thesame semiconductor layer. This is because, if the semiconductor layer isthus made continuous, the area used for wiring can be reduced, and theaperture ratio can be increased.

At this time, connection points between a plurality of active elementshaving the same polarity comprise common contact holes, and wiring isperformed from contact holes to active elements having a polaritydiffering from these active elements. This is because when the polarityis different, normal wiring must be performed. By this means, contactholes can be made common, and the area of occupation of connectionportions in the entire area of the driving circuit can be reduced.

In one embodiment described below, a plurality of active elements havingthe same polarity comprises second active elements, lightemission-controlling active elements, and current-controlling activeelements; however, the present invention is of course not limitedthereto.

As the gate terminals of the above second active elements and the abovecurrent-controlling active elements, common scan lines may be used; inthis case, with respect to common gate terminal connections, by usingscan lines without modification the wiring area can be reduced and theaperture ratio can be raised.

However, if the above second active elements and the abovecurrent-controlling active elements are not driven with the same timing,then of course different signal lines can be used as the respective gateterminals.

A third electro-optical device of this invention compriseselectro-optical elements, and peripheral circuitry driving the aboveelectro-optical elements; the above electro-optical elements are formedsuch that the boundaries of the electro-optical elements have at least aprescribed curvature, and at least a portion of the peripheral circuitsis formed in the region surrounded by the boundaries having at least theprescribed curvature and by polygonal boundaries circumscribing theelectro-optical elements.

A shape having a “prescribed curvature” is particularly effective whenelectro-optical elements are formed using liquid materials; in thiscase, it is desirable that the prescribed curvature be set according tothe viscosity and surface tension of the liquid material, and accordingto the material of the layer below the electro-optical elements.However, even in cases where the electro-optical elements are formed byevaporation deposition or other means without using liquid materials,there is the advantageous result that short-circuits are prevented.

It is preferable that a plurality of boundary portions having thisprescribed curvature be formed. It is also preferable that the pluralityof boundary portions thus formed be arranged essentially symmetricallywith respect to a center line passing through the geometric center ofthe electro-optical element.

For example, a portion of the peripheral circuit formed in this regionis a contact hole comprised by wiring of the peripheral circuit. It ispreferable that this contact hole be of polygonal shape compatible withthe shape of the region. A contact hole comprised by the wiring of theperipheral circuit is, for example, a contact hole which suppliescurrent to at least one of the electrodes of the electro-opticalelement. It is preferable that there be a plurality of contact holes,arranged essentially symmetrically with respect to a center line passingthrough the geometric center point of the above electro-optical element.

When using a liquid material to form electro-optical elements, byproviding an affinity-controlling layer which adjusts the affinity forthe liquid material near the boundaries of electro-optical elements, thefilm thickness of the functional layer constituting the electro-opticalelements can be controlled, and flatness can be improved. Also, bymaking the affinity for the liquid material of, at least, the walls ofthe bank layer different from that of the above affinity-controllinglayer, the effectiveness may be further increased. For example, bymaking the affinity for the liquid material of the walls of the banklayer lower than that of the affinity-controlling layer, the film formedby the liquid material no longer adheres to the walls of the bank layer,and the flatness of the film formed by the liquid material is furtherimproved.

This affinity-controlling layer may be formed so as to have astaircase-shape on the inside of the electro-optical elements withrespect to the walls formed by the bank layer.

Here a “bank” is a partition member to partition pixel regions. A bankis also effective for securing a distance from cathodes or commonelectrodes and data lines, scan lines, or other wiring which suppliessignals. By securing a sufficient distance, the parasitic capacitance isreduced, and delays when supplying signals can be suppressed.

In general, data signals are greatly affected by stray capacitances ofscan signals, which can cause operation delays, and so a sufficientdistance must be secured between data signals and common electrodes orcathodes.

It is preferable that, in boundary portions having a prescribedcurvature, at least one of the electrodes constituting theelectro-optical element be patterned according to the shape of theboundary portion. This is because, by patterning electrodes in a mannercompatible with the curvature, at least a portion of the peripheralcircuit can be arranged more easily. For example, at least a portion ofthe peripheral circuit is a contact region to enable connection betweenthe peripheral circuit and the above electrode.

A fourth electro-optical device of this invention comprises alight-emitting portion, and a peripheral circuit which controls thecurrent supplied to the above light-emitting portion via a pixelelectrode; the area of the above light-emitting portion is smaller thanthe area of the above pixel electrode, and the shape of the abovelight-emitting portion is different from the shape of the above pixelelectrode.

A fifth electro-optical device of this invention comprises alight-emitting portion, and a peripheral circuit which controls thecurrent supplied to the above light-emitting portion via a pixelelectrode; the area of the above light-emitting portion is smaller thanthe area of the above pixel electrode; the shape of the abovelight-emitting portion is a shape having a curvature, and the shape ofthe above pixel electrode is polygonal.

A sixth electro-optical device of this invention comprises alight-emitting portion, and a peripheral circuit which controls thecurrent supplied to the above light-emitting portion via a pixelelectrode; the area of the above light-emitting portion is smaller thanthe area of the above pixel electrode; the above light-emitting portionhas a polygonal shape having n vertices (where n is an integer equal to4 or greater); the above pixel electrode has a polygonal shape having mvertices (where m is an integer equal to 3 or greater); and the relationn>m obtains.

In the above electro-optical device, the light-emitting portion has ashape having a curvature, or has a polygonal shape with four or morevertices, so that short-circuits in the edge portions of light-emittingportion can be prevented. And when forming light-emitting portions usinga liquid material, the liquid material can be made to extend thoroughlyto the edge portions of light-emitting portions, so that a uniform filmcan be formed.

In the above electro-optical device, it is preferable that the entireregion of the above light-emitting portion be formed on the above pixelelectrode, and that a contact region for connection to the aboveperipheral circuit and to the above pixel electrode be provided in theportion of the above pixel electrode where the above light-emittingportion is not formed.

A seventh electro-optical device of this invention comprises anelectro-optical element, a holding capacitance which regulates thecurrent supplied to the above electro-optical element, and an activeelement which supplies a current according to the voltage recorded inthe holding capacitance; a first electrode constituting the holdingcapacitance is formed by patterning a portion of a metal layer whichforms a power supply line supplying current to the electro-opticalelement.

An eighth electro-optical device of this invention is configured toenable the supply of current to an electro-optical element by an activeelement according to the voltage recorded in a holding capacitance, andcomprises a first metal layer connected to a power supply, and a secondmetal layer patterned to comprise a portion of a control terminal of anactive element; a first electrode constituting the holding capacitanceis formed by patterning a portion of the first metal layer.

Here “layer” comprises, in addition to a metal layer, a layer whichaffects formation of the holding capacitance, such as for example asemiconductor layer.

A second electrode constituting the holding capacitance is formed bypatterning a portion of the metal layer which forms the control terminalof the active element.

In the above electro-optical device, the above first electrode may be aportion of the power supply line, and a portion of the metal layerforming the control terminal of the active element in a portion of thepower supply line may be overlapped in patterning to form the abovesecond electrode. By means of this configuration, there is no need inparticular to provide wiring to connect the holding capacitance and theactive element, so that the aperture ratio can be increased.

It is preferable that a semiconductor layer be comprised, overlappingelectrodes constituting the holding capacitance and formed in the shapeof the electrodes. This semiconductor layer may for example haveimpurities introduced. The semiconductor layer may be doped withimpurities to metallize or to lower the resistance.

It is preferable that the holding capacitance be formed in a regionother than the region in which the electro-optical element and activeelement are formed, so that the aperture ratio is raised. For example,each of the layers comprising the electrodes of the holding capacitancemay be formed on a polygon, such as for example a pentagon,corresponding to the shape of the region other than the region in whichare formed the electro-optical element and active element.

In the above electro-optical device, it is preferable that, of thelayers comprising the holding capacitance electrodes, the regionoccupied by the layer positioned on the lower side be formed to begreater than the region occupied by the layer positioned on the upperside.

In the above electro-optical device, the region occupied by the layerpositioned on the lower side is formed by patterning into a shape suchthat, even if the greatest possible position shift that can occur duringformation of the layer positioned on the upper side occurs, the regionof the layer positioned on the upper side is contained within the regionof the layer positioned on the lower side.

In the above electro-optical device, it is preferable that a bank layerbe further comprised in order to isolate neighboring electro-opticalelements, and that the holding capacitance be formed under the banklayer.

In addition, an affinity-controlling layer may be further comprised,within the bank layer or below the bank layer, in order to control theaffinity of the liquid material during formation of electro-opticalelements.

The overlap region in which is formed the holding capacitance may beprovided in a region in which at least one among the first metal layerand the second metal layer is formed in a power supply wiring pattern.

It is further preferable that the wiring pattern formed by the secondmetal layer be positioned at a prescribed distance or greater from atleast one among the two electrodes connected to the electro-opticalelement. By means of this configuration, unwanted capacitance can bereduced.

A fifth active matrix of this invention is an active matrix substratecomprising pixel electrodes and paths positioned corresponding to theintersections of data lines and scan lines; the above pixel electrodesare connected to a power supply line via at least one transistor; aholding element connected to the gate of the above one or moretransistors is provided; and a first electrode constituting the aboveholding element is connected to the above power supply line.

A sixth active matrix substrate of this invention is an active matrixsubstrate comprising pixel electrodes and paths positioned correspondingto the intersections of data lines and scan lines; the above pixelelectrodes are connected to a power supply line via at least onetransistor; a holding element connected to the gate of the above one ormore transistors is provided; and a first electrode constituting theabove holding element is a portion of the above power supply line.

In the above active matrix substrate, a second electrode constitutingthe above holding element is the gate of the above one or moretransistors.

A seventh active matrix substrate of this invention is an active matrixsubstrate comprising unit circuits each comprising a transistor,corresponding to the intersections of scan lines and data lines; asemiconductor film constituting the above transistors is formed in asemiconductor layer; at the intersections of the above scan lines andthe above data lines, either the above scan line or the above data lineis formed in a first conducting layer; and the portions of the abovescan line and the above data line other than at the above intersectionare formed in a second conducting layer. In this active matrixsubstrate, it is preferable that the above second conducting layer bepositioned between the above first conducting layer and the abovesemiconductor layer.

By combining the above active matrix substrate with electro-opticalelements, an electro-optical device can be configured.

A ninth electro-optical device of this invention is an electro-opticaldevice comprising electro-optical elements corresponding to theintersections of scan lines and data lines; either the above scan linesor the above data lines are formed in a first conducting layer at theintersections of the above scan lines and the above data lines, togetherwith a pair of electrodes which supply power to the aboveelectro-optical element; the portions of the above scan lines and theabove data lines other than in the above intersections are formed in asecond conducting layer; and the above second conducting layer ispositioned at a greater distance than the above first conducting layerfrom one of the above pair of electrodes.

Here, the above electro-optical elements may be electroluminescence (EL)elements. “Electroluminescence elements” refer in general to elements,whether employing an organic or an inorganic (such as Zn:S)light-emitting material, which utilize electroluminescence phenomena inwhich the application of an electric field causes holes injected from ananode and electrons injected from a cathode to recombine, so that therecombination energy causes the light-emitting material to emit light.As the layer structure enclosed between the electroluminescence element,in addition to a light-emitting layer comprising light-emittingmaterial, a hole transport layer or an electron transport layer, orboth, may also be comprised. Specifically, as layer structures, inaddition to a cathode/light-emitting layer/anode structure, acathode/light-emitting layer/hole transport layer/anode,cathode/electron transport layer/light-emitting layer/anode,cathode/electron transport layer/light-emitting layer/hole transportlayer/anode, or similar may be adopted.

The above active matrix substrates may also be employed in electronicdevice. Here there is no particular restriction on “electronic device”,which includes a device comprising a display device comprising an activematrix substrate, such as for example portable telephones, videocameras, personal computers, head-mounted displays, rear- orfront-projectors, and also fax machines with display functions, theviewfinder of digital cameras, portable TV sets, DSP devices, PDAs,electronic organizers, and similar.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall drawing of a display panel of this embodiment;

FIG. 2 is a plane view of a pixel region in embodiment 1;

FIG. 3 shows plane views of a pixel region in embodiment 1; FIG. 3A is across-section along A-A in FIG. 2, FIG. 3B is a cross-section along B-Bin FIG. 2, and FIG. 3C is a cross-section along C-C in FIG. 2;

FIG. 4 shows examples of modification of the boundary shape of thelight-emitting portion; FIG. 4A shows the case of a circularlight-emitting portion, FIG. 4B shows the case of a light-emittingportion having a curved portion symmetrical about a center line, andFIG. 4C shows the case of a light-emitting region having a curvedportion asymmetrical about a center line;

FIG. 5 is a circuit diagram of a pixel region in embodiment 1;

FIG. 6 is a drawing explaining the alignment of a metal layer inembodiment 1;

FIG. 7 is a drawing explaining processing to separate gate metal inembodiment 1;

FIG. 8 is a plane view of a pixel region in embodiment 2;

FIG. 9 shows cross-sectional views of a pixel region in embodiment 2;FIG. 9A is a cross-section along A-A in FIG. 8, FIG. 9B is across-section along B-B in FIG. 8, and FIG. 9C is a cross-section alongC-C in FIG. 8;

FIG. 10 is a plane view of a pixel region in embodiment 3;

FIG. 11 shows cross-sectional views of a pixel region in embodiment 3;FIG. 10A is a cross-section along A-A in FIG. 10, and FIG. 10B is across-section along B-B in FIG. 10;

FIG. 12 is a plane view of a pixel region in embodiment 4;

FIG. 13 shows cross-sectional views of a pixel region in embodiment 4;FIG. 13A is a cross-section along A-A in FIG. 12, and FIG. 13B is across-section along B-B in FIG. 12;

FIG. 14 is a connection diagram for a display panel in embodiment 5;and,

FIG. 15 shows examples of electronic device in embodiment 5, showingexamples of application of a display panel of this invention to aportable telephone in FIG. 15A, to a camcorder in FIG. 15B, to aportable personal computer in FIG. 15C, to a head-mounted display inFIG. 15D, to a rear projector in FIG. 15E, and to a front projector inFIG. 15F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, preferred embodiments of the invention are explained, referring tothe drawings as examples. The following embodiments are no more thanexamples of embodiments of this invention, and do not limit the scope ofapplication.

Embodiment 1

This embodiment of the invention relates to a display panel which is anelectro-optical device employing EL elements as electro-opticalelements. FIG. 1 is an overall drawing of a display panel comprising anactive matrix panel, comprising EL elements.

As shown in FIG. 1, the display panel 1 is configured by positioning adisplay region 11 and driver regions 14 and 15 on a glass substrate 16.A cathode 12 is formed over the entirety of the display region 11, andis connected to the cathode lead electrode 13. Pixel regions 10 arearranged in a matrix in the display region 11. In the case of a colordisplay, the pixel regions 10 are configured to enable emission ofprimary colors (for example, the three primary colors red, blue, green)taken as necessary for color display; a combination of pixel regionsemitting light of each primary color becomes one pixel element. Forexample, the driver region 15 positioned in the column direction of thedisplay region 11 outputs a write control line Vsel and a light emissioncontrol line Vgp; and the driver region 14 positioned in the rowdirection of the display region 11 outputs, in addition to the powersupply line Vdd, data current signals to the data line Idata. Bycontrolling the light-emission state in each pixel region 10 by means ofdriver circuits, not shown, formed in the driver regions 14 and 15, anarbitrary image can be displayed in the display region 11.

FIG. 2 shows a plane view which explains the wiring pattern in one pixelregion and the periphery. In FIG. 2, the patterns can be seen in thesemiconductor layer 102, which is particularly important and is shown inFIG. 3, in the gate metal layer 104, source metal layer 106, and anodelayer 110.

As shown in FIG. 2, the light-emitting portion OLED and peripheralcircuitry to drive this portion are all positioned in the regionenclosed by the power supply line Vdd and the data line Idata. The powersupply line Vdd is positioned at a distance from the data line Idata,with the light-emitting portion OLED intervening. The peripheral circuitcomprises a transistor T1 as a first active element, a transistor T2 asa second active element, a transistor T3 as a current-controlling activeelement, a transistor T4 as a light emission-controlling active element,and a holding capacitor C as a holding element. No restrictions inparticular are placed on the conduction types of the transistors T1 toT4, but in this embodiment, the conduction type of transistor T1 is ptype, and that of all the other transistors is n type.

The source of the transistor T1 is connected to the power supply lineVdd, and the drain is connected to the drain side of transistor T4. Thesource of transistor T4 is connected to the anode of the light-emittingportion OLED. The holding capacitor C is formed between the power supplyline Vdd and the gate of transistor T1. The source of transistor T2 isconnected to the holding capacitor C and to the gate of transistor T1,and the drain is connected to the drain of transistor T3 and betweentransistors T1 and T4. The source of transistor T3 is connected to thedata line Idata, and the gate is connected, in common with the gate oftransistor T2, to the write-control line Vsel.

FIG. 3 shows cross-sections to explain the layer structure in each ofthe cross-sectional planes shown in FIG. 2. FIG. 3A, FIG. 3B, and FIG.3C show the layer structure in the A-A cross-sectional plane, B-Bcross-sectional plane, and C-C cross-sectional plane, respectively.

As shown in FIG. 3A, the pixel region 10 is configured by stacking, onthe glass substrate 100 (the glass substrate 16 in FIG. 1), anunderlayer protection film 101, semiconductor layer 102, gate insulatingfilm 103, gate metal layer 104, first interlaminar insulating film 105,source metal layer 106, second interlaminar insulating film 107, banklayer 108, and cathode layer 109 (the cathode 12 in FIG. 1). Further, asshown in FIG. 3B and FIG. 3C, the electric field light-emitting portionOLED is configured by stacking an anode layer 110, hole transport layer111, and light-emitting layer 112.

As the glass substrate 100, because the EL elements of this embodimentemit light on the substrate side and it is necessary that light betransmitted, soda lime glass, low-expansion glass, quartz glass, andother non-alkaline glasses are employed. However, when an opticallytransmissive material is used as the cathode layer 109 and EL elementsare configured such that light is emitted from the cathode side, it isalso possible to use metal or other conductive materials, as well assilicon carbide (SiC), alumina (Al₂O₃), aluminum nitride (AlN), andother non-transparent insulating materials.

As the underlayer protective film 101, silicon oxide film (SiO_(x):0<x≦2), silicon nitride film (Si₃N_(x): 0<x≦4), and other insulatingmaterials can be used. The underlayer protective film is formed in orderto prevent sodium (Na) and other mobile ions contained in the glasssubstrate from penetrating into the semiconductor layer and exertingadverse effects on impurity control in the semiconductor layer.

After first washing the substrate 100 with deionized water and alcoholor another organic solvent, the underlayer protection layer 101 isformed on the substrate by atmospheric-pressure chemical vapordeposition (APCVD), low-pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), or another CVDmethod, or by sputtering.

As the semiconductor layer 102, in addition to a group IV single-elementsemiconductor layer of silicon (Si), germanium (Ge) or similar, acomplex with a group IV element, such as silicon germanium(Si_(x)Ge_(1-x): 0<x<1), silicon carbide (Si_(x)C_(1-x): 0<x<1), orgermanium carbide (Ge_(x)C_(1-x): 0<x<1), as well as a compound of groupIII and group V elements such as gallium arsenide (GaAs) and indiumantimonide (InSb), a compound of group II and group VI elements such ascadmium selenide (CdSe), or other different complex compounds such assilicon germanium gallium arsenide (Si_(x)Ge_(y)Ga_(z)As_(z): x+y+z=1),can be employed.

The semiconductor layer 102 is formed by first depositing silicon orsimilar by, for example, the APCVD, LPCVD, PECVD or other CVD method, orby sputtering, evaporation deposition, or other PVD method, and thenirradiating with laser light to induce a polycrystalline structure. Asthe laser light, the fundamental and higher harmonics of an excimerlaser, argon ion laser, or YAG laser are used as appropriate. Forexample, when a polycrystalline structure is induced in silicon,polysilicon is obtained. This polycrystalline semiconductor layer 102 ispatterned so as to be compatible with the element shapes of the holdingcapacitance C and each of the TFTs (thin film transistors) T1 to T4. Forexample, by performing reactive ion etching using a mixture of CF₄ andoxygen gases, a semiconductor layer in an amorphous state can bepatterned into an island morphology compatible with element shapes.After patterning, for example, a gate metal layer is formed, and thenthe gate metal layer is used as a mask to introduce impurities into thesemiconductor layer. Specifically, phosphorus (P), arsenic (As),antimony (Sb), or other donor elements are added for each element toobtain n-type semiconductor layer, and boron (B), aluminum (Al), gallium(Ga), indium (In), and other acceptor elements are added to obtainp-type semiconductor layer. In this embodiment, impurities areintroduced such that the semiconductor layer constituting the holdingcapacitor C are n-type semiconductor layer. When TFTs with an LDDstructure are employed and the threshold voltage of the TFTs is to beadjusted, channel doping to introduce impurities in low concentrationsis performed.

As the gate insulating film 103, for example, a silicon dioxide film isformed using tetraethyl orthosilicate (TEOS) as the raw material. Thegate insulating film 103 is formed by, for example, plasma CVD in amicrowave-discharge plasma, ECR plasma, or other oxygen or nitrogenatmosphere.

As the gate metal layer 104, a conductive material such as, for example,tantalum (Ta), tungsten (W), chromium (Cr), or aluminum (Al) is used.The gate metal layer 104 is formed by first depositing a film bysputtering or other means, and then patterning into the shape of a gateelectrode.

As the first interlaminar insulating film 105, silicon oxide, siliconnitride, or some other insulating film can be used. The firstinterlaminar insulating film is formed by sputtering or similar, and,for example, contact holes are then formed in order to form TFT sourceand drain electrodes.

As the source metal layer 106, in addition to aluminum (Al), forexample, tantalum, molybdenum, titanium, tungsten, or some otherconductive material can be used. The source metal layer is formed byusing sputtering or another method to uniformly layer a conductivematerial, and then patterning according to the electrode shape.

As the second interlaminar insulating film 107, silicon oxide, siliconnitride, or some other insulating film can be used. The secondinterlaminar insulating film is formed by sputtering or other means, andthen, for example, contact holes h1 and h2 for the anode layer 110 areformed.

As the anode layer 110, for example, indium tin oxide (ITO) alloy orsome other optically transmissive conducting material can be used. Whenthere is no need for optical transmission properties, tin oxide (NESA),gold, silver, platinum, copper, or another material can be used as theanode layer. After using sputtering or some other method to form theanode layer, patterning is performed according to the shape of thelight-emitting portion OLED. No restrictions in particular are placed onthe shape of the anode layer (or the pixel electrodes), but it isdesirable that the area be larger than that of the light-emittingportion OLED. Through such a configuration, a contact region forelectrical connection of a peripheral circuit or pixel circuit with thepixel electrodes can be provided in a region other than thelight-emitting portion of the pixel electrodes. Through such aconfiguration, the flatness of, at least, the light-emitting portion canbe improved.

As the bank layer 108, silicon oxide, silicon nitride, polyimide, orsome other insulating material can be employed. The bank layer is formedby deposition using sputtering or a similar method, after which anaperture portion is provided in a position corresponding to thelight-emitting portion OLED.

As the hole transport layer 111, for example,N,N′-diphenyl-N,N′-bis-(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TPDA) is used. The hole transport layer is deposited in the apertureportion provided in the bank layer 109, using a metal mask or similar.

As the light-emitting layer 112, for example, tris-(8-quinolinol)aluminum (Alq₃) or another arbitrary light-emitting material is used.The light-emitting layer can be formed by evaporation deposition using ametal mask or silicon mask; however, an ink jet method may be employedto arrange a solvent comprising the light-emitting material in theaperture portion, after which the solvent component is caused toevaporate.

As the cathode layer 109, a material the energy level of which enablesuse as the cathode of an EL element, such as aluminum or an alloy ofaluminum with another element (such as lithium), or calcium or similar,is used. The cathode layer is formed using a metal mask or similar, andis patterned by photolithography or using a shadow mask method.

In this embodiment, pixel electrodes are anodes and the common electrodeis a cathode; however, a configuration may be employed in which thepixel electrodes are cathodes and the common electrode is a anode.Typically, cathode materials are often metals, but when the pixelelectrodes are cathodes, the light emitted by the light-emitting portionOLED is then emitted on the side opposite the substrate 100. Of course,even when the pixel electrodes are anodes and the common electrode is acathode, by using a transparent material as the cathode material, or bymaking the film thickness sufficiently thin that light is transmitted,light can be emitted on the side opposite the substrate 100.

Below, several features regarding wiring patterns in this embodiment areexplained in sequence.

Planar Shape of the Light-Emitting Portion

One method of manufacture of EL elements involves using an ink jetmethod to discharge a liquid material comprising a light-emittingmaterial, carrier transport material or carrier blocking material intoan aperture portion, followed by drying, to form the light-emissionlayer. In this manufacturing method, it is important that the dischargedliquid material extend uniformly to all areas of the aperture portion.If the liquid material does not extend uniformly, the thickness of thelight-emitting layer after film deposition is uneven, the intensity oflight emitted within the light-emitting region is uneven, and the imagequality of the display panel is diminished. If for example it issupposed that the planar shape of the aperture portion is square, thenunder the influence of the surface tension and viscosity of the liquidmaterial, the height of the surface of the liquid material dischargedinto the corners of the aperture portion will differ from other areas.Hence there is the possibility that for a light-emitting portion withsuch a shape, the thickness of the light-emitting layer after filmformation will be uneven.

On the other hand, there is a need to increase the brightness of thedisplay panel, and so there are requests to increase insofar as possiblethe size of the region in which light is emitted, that is, thelight-emitting portion, and to reduce insofar as possible the regionoccupied by peripheral circuitry, that is, to raise the aperture ratio.The pattern layout cannot be designed considering only the ease ofmanufacture.

In order to satisfy all these requests, in this embodiment theboundaries of the light-emitting portion are formed so as to have atleast a prescribed curvature, and at least a portion of the peripheralcircuit is formed in the region surrounded by these boundaries havingthe prescribed curvature and the boundaries of a polygon circumscribingthe boundaries of this light-emitting portion.

Based on FIG. 4, a specific concept is explained. FIGS. 4A, 4B and 4Cshow, partially or entirely, the planar shape of a light-emittingportion to which the concept of this invention is applied. FIG. 4A isthe case in which the boundary of the light-emitting portion iscircular, that is, the entire boundary has a fixed curvature R. Aportion of the peripheral circuit is provided within the region,indicated by shading, enclosed by this circle and by a polygoncircumscribing the circle, that is, the square shown by a broken line.The light-emitting portion of this circle is regarded as having an idealshape for rendering uniform the film thickness of the light-emittingportion, insofar as the shape is symmetrical about any center linepassing through the center. However, as shown in FIG. 4A, effectiveutilization of the shaded portion is necessary in order to improve theaperture ratio of the light-emitting portion.

FIG. 4B is an example in which this invention is applied to the cornersof a rectangular shape; in this example, the boundaries of thelight-emitting portion are provided with a fixed curvature R. In thisexample, the circumscribing polygon is a rectangle, shown by a brokenline; the shaded regions surrounded by the boundaries of thelight-emitting portion and the boundaries of the rectangle are theregions in which a portion of, or the entirety of, the peripheralcircuit is provided. The present embodiment pertains to this example; asthe curvature R is increased, an oblong planar shape for thelight-emitting portion results, such as in this embodiment. In thisexample also, the shape is symmetrical laterally and vertically about acenter line passing through the center of the light-emitting portion,and moreover the curvature of the corner portions is equal to or greaterthan a fixed value, so that a light-emitting portion with uniform filmthickness can be formed.

FIG. 4C is an example in which the curvature of the corner portions isset to be unequal with respect to a center line. The curvature R1 of thecorner portion on the left side facing the drawing is smaller than thecurvature R2 of the corner portion on the right side.

In this example, the circumscribing polygon is a rectangle, shown by abroken line, and the shaded regions surrounded by the boundaries of thelight-emitting portion and the boundaries of the rectangle are regionsin which a portion of or the entirety of the peripheral circuit isprovided. Even when the curvature is unequal in this way, by setting theminimum curvature to be greater than or equal to a constant value, alight-emitting portion with uniform film thickness can be formed.Because the minimum curvature is affected by the viscosity and surfacetension of the discharged solution, and by the water repellence orliquid repellence (affinity to water or to liquids) of the dischargesurface, the minimum curvature should be determined by experiment foreach set of conditions.

In this embodiment, a light-emitting portion with a rectangular planarshape, such as shown in FIG. 2, is adopted. And, a portion of theperipheral circuit, namely, the contact holes h1 and h2 (see FIG. 3B),is formed within the region surrounded by the boundaries of thelight-emitting layer and the boundaries of the rectangle (not shown)circumscribing the boundaries of the light-emitting portion. In thisembodiment, the regions indicated by shading in FIG. 4B which normallyare wasted space are used for these contact holes, and this satisfydemands for effective use of space.

In addition to contact holes, any other elements of the peripheralcircuit, such as for example transistors and capacitors, may be formedin the regions surrounded by the boundaries of the light-emittingportion and the boundaries of a polygon circumscribing thelight-emitting portion. Moreover, it is not necessary to include theentirety of an independently functioning element in these regions; aportion of an element or contact, that is, a portion of the peripheralcircuit, may be included in the region. In other words, it is essentialthat placement be performed so as to make effective use of space.

In cases where a liquid material is not used to form the light-emittingportion, even when, for example, evaporation deposition or similar isused to form the light-emitting portion, by employing a shape in whichthe edge portions of the light-emitting portion have a curvature, thereis the enduring advantage that the danger of short-circuits between thepixel electrode at the edge portions of the light-emitting portion OLEDand the common electrode is reduced.

Strictly speaking, a curvature can be represented as a collection offine straight lines, and so the shape of the light-emitting portion canbe interpreted as a polygon having more numerous vertices than the shapeof the pixel electrode.

Contact Holes for the Light-Emitting Portion

In an EL element, provision of a contact hole in a region surrounded bythe boundaries of the light-emitting portion and the boundaries of apolygon circumscribing the light-emitting portion, as shown in FIG. 2,is significant. In other words, by providing a comparatively largecontact hole in this region, the region can be used effectively, andsufficient current can be supplied to the light-emitting portion.

It is further preferable that a plurality of contact holes be provided.That is, in the EL element, a certain amount of current in thelight-emitting layer must be passed uniformly to the entirety of thelight-emitting portion. If a contact hole used for connection to ananode directly supplying current is provided in an eccentric position,the supply of current may be uneven. An uneven supply of current appearsas irregularities in the intensity of light emission.

If, as in this embodiment, a plurality of contact holes are provided inpositions which are symmetrical with respect to a center line passingthrough the center of the light-emitting portion, then this problem canbe resolved. That is, as shown in FIG. 2, in this embodiment a pluralityof comparatively large contact holes are provided in regions providedsymmetrically with respect to a prescribed center line passing throughthe center of the light-emitting portion. By providing these contactholes in symmetrical regions, the demand for uniform film deposition inthe light-emitting portion, as well as the demand that current suppliedto the light-emitting portion be uniform, can both be satisfied.

Alignment of Metal Layers

Depending on the EL element driving method, the stability of the currentsupplied to the light-emitting portion may be affected by fluctuationsin the holding capacitance. In this embodiment also, it is undesirablefor the capacitance value of the holding capacitor C to fluctuationeither from one pixel to another, or from one display panel to another.However, when stacking metal layers in a process to manufacture adisplay panel, there may occur shifts from planned positions. Becausethe numerical area of overlapping metal layers determines the holdingcapacitance, shifts in position give rise to fluctuations or scatteringin capacitance values, and there are cases in which capacitance valuesof holding capacitances may cause fluctuations either among pixelregions, or among display panels.

Hence in this embodiment, in the vicinity of overlapping regions formingthe holding capacitor C, among the plurality of layers related toformation of the holding capacitor C, that is, among the source metallayer 106, gate metal layer 104, and semiconductor layer 102, theoccupied region or width of a layer positioned on the lower side(relative to the source metal layer, the gate metal layer andsemiconductor layer) is formed to be larger than the occupied region orwidth of the layer positioned on the upper side (relative to thesemiconductor layer, the gate metal layer and source metal layer;relative to the gate metal layer, the source metal layer).

This feature can be seen in the plane view of FIG. 2, but is explainedin greater detail referring to the A-A cross-section shown in FIG. 6. Asshown in FIG. 6, if the width of the source metal layer 106 is d1, thewidth of the gate metal layer 104 is d2, and the width of thesemiconductor layer 102 is d3, then the relation d3>d2>d1 obtains. Thelower the layer, the larger is the pattern shape.

The extent to which [the pattern shape] should be increased will varydepending on the precision of the manufacturing processes and thepattern density. As one approach, patterns should be formed for eachlayer such that, when forming layers positioned on the upper side, evenwhen the maximum possible shift in position occurs, the region in thelayer positioned on the upper side will be contained within the regionin the layer positioned on the lower side. In this embodiment also, thedifferences d3−d2 and d2−d1 are designed to be equal to or greater thanpredicted position shifts in manufacturing processes.

Formation of Separations between Gate Metal Layers

EL elements comprise a common electrode; the common electrode is formedover the entirety of the display region. In this embodiment also, acathode 13 (cathode layer 109) is formed over the entirety of thedisplay region 11 as shown in FIG. 1 as the common electrode for thelight-emitting portion OLED. However, if the common electrode is formedover the entirety, there is the problem that a capacitance occurs withthe gate metal layer connected to the gates of transistors. If suchstray capacitance appears, lags occur in transistor operation, andoperation with the timing of the design cannot be guaranteed.

Hence in this embodiment, the wiring pattern formed by the gate metallayer is positioned with a separation of at least a prescribed distancefrom at least one among the electrodes of the light-emitting layer. Aproblem due to low impedance arises due to the distance between thecathode layer 109 which is the common electrode and the gate metal layer104. Also, the cathode layer 109 is a small distance from the lower sidein the light-emitting portion OLED, so that the distance from the gatemetal layer in the vicinity of the light-emitting portion poses aproblem. Hence in this embodiment, as shown in FIG. 7 (equivalent to theC-C cross-section in FIG. 2), patterns are formed such that, near thelight-emitting portion, the distance d1 in the depth direction betweenthe cathode layer 109 and the gate metal layer 104 and the distance d2in the plane are both equal to or greater than a prescribed distance.

Here the prescribed distance will change variously depending on the areaof the gate metal layer and the dielectric constants of interveninglayers, and so cannot be specified generally; however, it is preferablethat patterning should be at as great a distance as possible, within therange allowed by the area of pixel regions and other.

Wiring to supply data signals, scan signals, and other electricalsignals must be laid out in consideration of operation delays caused bystray capacitances. In this embodiment, the data lines Idata and scanlines Vsel use the gate metal layer 104 which is at a greater distancefrom the cathode 109 which is a common electrode, and at theintersections between data lines Idata and scan lines Vsel, data linesIdata are formed in the source metal layer 106, but the portions of datalines Idata outside intersections and the scan lines Vsel are formed inthe gate metal layer 104.

When it is necessary to further reduce the stray capacitances to whichdata lines Idata contribute, the entirety of the data lines Idata may beformed in the conducting layer which is at the greatest distance fromthe common electrode. To give an explanation corresponding to thisembodiment, at the intersections between data lines Idata and scan linesVsel, scan lines Vsel are formed in the source metal layer 106, and theentirety of data lines Idata as well as the portion of scan lines Vseloutside intersections may be formed in the gate metal layer 104.

In order to remove signals lines such as scan lines and data linesfarther from the common electrode and from pixel electrodes, aconducting layer may be formed in the same layer as the semiconductorlayer 102; and, if a so-called bottom-gate configuration for transistorsis employed, then the conducting layer may be provided below thesemiconductor layer, and this conducting layer can be used for wiring ofsignal lines.

Operation of Peripheral Circuits

Next, the operation of the peripheral circuit of an EL element of thisembodiment is explained. FIG. 5 shows a circuit diagram for one pixelcircuit constituting the pixel region 10.

1) The circuit of this embodiment has a circuit configuration whichoperates through the supply of current data as data signals. Pixeldisplay begins with the selection of the write control line Vsel as adata writing operation, putting the transistors T2 and T3 into theturned-on state.

2) When the transistors T2 and T3 are put into the conducting state, thetransistor T1 reaches a steady state after a prescribed time, andelectric charge accumulates in the holding capacitor C according to thedata current Cdata.

3) As light emission action, the write control line Vsel is put into theunselected state, the transistors T2 and T3 are turned off, and afterstopping supply of the data current Cdata, the light emission controlline Vgp is selected. As a result, the transistor T4 is turned on, and acurrent corresponding to the potential difference Vgs between thevoltage stored in the holding capacitor C and the power supply voltageVdd is supplied to the light-emitting portion OLED via the transistorsT1 and T4, so that light is emitted from the light-emitting layer.

Improvement of Current Maintenance Performance in Peripheral Circuits

Below, features of this embodiment in the peripheral circuitry areexplained.

In the prior art, no consideration in particular has been paid to activeelements controlling the charging and discharging of holdingcapacitances. In miniaturized FETs, when the gate voltage is below thethreshold, the drain current also depends on the drain voltage. That is,the injection current in the source-drain channel increases as anexponential function of the gate voltage, and leakage currents occur.For example, when a leakage current occurs in transistor T2 shown inFIG. 5, the cross-terminal voltage Vgs of the holding capacitor Cdeviates from the value corresponding to the supplied data signal, andthe drain current of the transistor T1 which takes this voltage as acontrol voltage for input to its gate fluctuates. This fluctuationappears as a change in brightness in the light-emitting portion OLED, sothat light emission at a stable brightness can no longer be guaranteed.

Hence in this embodiment, as shown in FIG. 1 and FIG. 5, transistor T2which is an active element directly connected to the holding capacitor Cis an active element with multiple control terminals, that is, amulti-gate type transistor. Using such a transistor, as indicated by thearrow in FIG. 5, is for practical purposes equivalent to directlyconnecting a plurality of transistors, and the leakage current isgreatly suppressed. A current corresponding to the supplied data signalis reliably supplied to the light-emitting portion OLED.

As the transistor T2, instead of, or in addition to, a multi-gate typestructure, an LDD, GDD, or DDD structure can also be employed. Byemploying such a structure, the leakage current can be reduced, andadverse effects due to hot electrons when a FET is miniaturized aresuppressed, so that element reliability is enhanced.

In this embodiment, in consideration of the polarity of control signals,transistor T1 and transistor T2 have opposite polarities, that is,transistor T1 is a p-type FET, and transistors T2 to T4 are n-type FETs.However, whether to use a p-type or an n-type [transistor] can bedecided arbitrarily according to the polarity and other details ofsignals which are to be used, and no restrictions apply.

Moreover, the placement of elements is not limited to that of FIG. 5.For example, the electrical potential relationships of the holdingcapacitor, transistor T1, and light-emitting portion OLED can bereversed. In this case, it is desirable that the common electrode of thelight-emitting portion be an anode, and that the polarities of each ofthe transistors (whether n-type or p-type) be reversed.

Reduction of Peripheral Circuit Space

As explained above, in order to increase the brightness or apertureratio in a display device, it is demanded that the region occupied byperipheral circuitry be decreased as much as possible. To this end, inthis embodiment a wiring pattern is formed such that at least one activeelement among the plurality of transistors and other active elements isconnected to another active element by the same contact hole.Specifically, as shown in FIG. 2, transistors T2, T3, and T4 areinterconnected by the same contact hole h3. In this way, the layout isoptimized such that there are more numerous common connection points orcontacts in a circuit, and by arranging elements such that portionswhich are common contact points are connected by the same connectionpoints, the number of contact holes can be reduced and the area occupiedby the peripheral circuitry is reduced due to these contact holes.

Embodiment 2

FIG. 8 shows a plane view explaining one pixel region and the wiringpattern in the vicinity thereof for an EL element of embodiment 2 ofthis invention. FIG. 9 shows cross-sectional views which explain thelayer structure in cross-sections of FIG. 8. FIG. 9A shows the layerstructure in a cross-section along the A-A plane, FIG. 9B is across-section along B-B, and FIG. 9C is a cross-section along C-C. Inthese drawings, similarly to embodiment 1, the patterns of the principalsemiconductor layer 102, gate metal layer 104, source metal layer 106,and anode layer 110 are shown.

The configuration of the EL element in embodiment 2 is, except for theexistence of an affinity-controlling film 113 which forms a step shape,similar to the EL element of embodiment 1. Hence components similar tothose of embodiment 1 are assigned the same symbols in the drawings, andexplanations are omitted.

Below, features of this embodiment are described.

Affinity-Controlling Layer

As shown in FIG. 9C, the light-emitting portion OLED in embodiment 2comprises an affinity-controlling layer 113, between the secondinterlaminar insulating film 107 and the bank layer 108. Thisaffinity-controlling layer 113 need not be formed over the entire pixelregion, but when forming a light-emitting portion OLED using a liquidmaterial, should preferably be provided at least near the boundaries ofthe light-emitting portion. The affinity-controlling layer 113 must havean affinity for the liquid material used in forming the light-emittingportion. In this embodiment, the bank layer 108 forms a wall near theboundary of the light-emitting portion; a material is selected whichexhibits no affinity for the liquid material used when forming thelight-emitting layer 110, and [the bank layer] is stacked on top of theaffinity-controlling layer 113. Consequently the affinity-controllinglayer 113 forms a step shape Step on the inside of the light-emittingportion in the wall formed by the bank layer, as shown in FIG. 8 andFIG. 9C.

The material of the affinity-controlling layer 113 is determinedaccording to the kind of properties of the liquid material which is usedto fill the light-emitting region by the ink jet method. For example, ifthe liquid material comprises a liquid such as water which is highlypolar, it is desirable that the affinity-controlling layer have polarbases, at least in the portion making contact with the liquid materialor on the surface. Conversely, if the liquid material comprises anonpolar liquid, it is desirable that the affinity-controlling layerhave nonpolar bases, at least in the portion making contact with theliquid material or on the surface. Also, the extent of the affinity ofthe affinity-controlling layer is determined by the surface tension ofthe liquid material which fills the light-emitting region.

For example, even if a material which chemically has a weak affinity forwater is used as an affinity-controlling layer, if the liquid materialcomprises large quantities of a solvent with a surface tension lowerthan that of water, the surface tension of the liquid material will belower than that of water, and so the affinity-controlling layer willexhibit affinity for the liquid. Hence the type of material to use inthe affinity-controlling layer is changed variously according to theliquid material to be used.

It is preferable that the affinity-controlling layer 113 comprise aninorganic compound or organic compound which in turn comprises one amongAl, Ta or another metal, silicon oxide, silicon nitride, amorphoussilicon, polysilicon, polyimide, an organic compound with fluoridebonds, or a photoresist. If insulating properties are necessary, theaffinity-controlling layer comprises a nonmetallic compound. Theaffinity of these materials is determined by differences in the contactangle with respect to the liquid material. That is, the degree ofaffinity or absence of affinity is determined in relative and notabsolute terms. The degree of affinity can also be adjusted throughsurface treatment methods.

It is preferable that the bank layer 108 comprise a material with weakeraffinity than the affinity-controlling layer 113. This is because, bymaking the affinity of the bank layer weaker than that of theaffinity-controlling layer, the absence of affinity of the bank layercan repel the liquid material to prevent flowing of the liquid materialinto neighboring pixel regions and avoid short-circuits. Also, theabsence of affinity of the bank layer prevents liquid material frombeing drawn excessively toward the bank layer side so that aconcave-shape film is formed.

Thus in this embodiment, an affinity-controlling layer with an affinityfor the liquid material is provided near the boundaries of thelight-emitting portion, so that a light-emitting layer of uniform filmthickness can be formed.

In this way, according to this embodiment, an affinity-controlling layerwith affinity for the liquid material is provided near the boundaries ofthe light-emitting portion, so that the uniformity of the thickness ofthe hole injection layer, light-emitting layer, and other layersconstituting the light-emitting portion is improved.

In this embodiment, the affinity-controlling layer 113 is formed in astep shape; but when the thickness of the layer cross-section can bemade sufficiently great, walls without a step shape, that is, a singlewall without a step with the bank layer, may be formed.

Other advantageous results of embodiment 2 are similar to those ofembodiment 1, and an explanation is omitted.

Embodiment 3

FIG. 10 shows a plane view which explains one pixel region and theperipheral wiring pattern for an EL element in embodiment 3. FIG. 11shows cross-sectional views explaining the layer structure incross-sections indicated in FIG. 10. FIG. 11A and FIG. 11B show thelayer structures in the cross-sections along A-A and B-B respectively inFIG. 10. In these drawings, similarly to embodiment 1, patterns in theprincipal semiconductor layer 202, gate metal layer 204, source metallayer 206, and anode layer 210 can be seen.

In the pattern shape of the EL element in embodiment 3, the width of thepixel region 20 is smaller than the width of the pixel region 10 inembodiment 1. However, the circuit configuration is similar to that ofembodiment 1 (see FIG. 5), and the materials forming each layer are alsosimilar to embodiment 1, and so components which are the same as inembodiment 1 are assigned the same symbols in the drawings, andexplanations are omitted. The glass substrate 100, underlayer protectionfilm 101, semiconductor layer 102, gate insulating film 103, gate metallayer 104, first interlaminar insulating film 105, source metal layer106, second interlaminar insulating film 107, bank layer 108, cathodelayer 109, anode layer 110, hole transport layer 111, and light-emittinglayer 112 in embodiment 1 correspond, respectively, to the glasssubstrate 200, underlayer protection film 201, semiconductor layer 202,gate insulating film 203, gate metal layer 204, first interlaminarinsulating film 205, source metal layer 206, second interlaminarinsulating film 207, bank layer 208, cathode layer 209, anode layer 210,hole transport layer 211, and light-emitting layer 212 in embodiment 3.Also, the transistors T1 to T4 in embodiment 1 correspond respectivelyto the transistors T11 to T14 in embodiment 3, and the contact holes h1to h3 in embodiment 1 correspond respectively to the contact holes h11to h13 in embodiment 3.

Below, features of the wiring pattern in this embodiment are explained.

Holding Capacitor Under the Power Supply Line

In embodiment 1, the holding capacitor C was positioned between thepower supply line Vdd and the data line Idata, outside thelight-emitting portion (in the upper portion of the light-emittingportion in FIG. 2). However, when the area of the pixel region iscomparatively small as in this embodiment, that is, when the pixeldensity is high, it is not possible to secure sufficient element spacefor occupation by the holding capacitor.

Hence in this embodiment, the holding capacitor C is formed in theregion in which at least one among a first metal layer (for example, thesource metal layer 206) or a second layer forms a power supply wiringpattern. Specifically, as shown in FIG. 10, the holding capacitor C isformed by stacking a gate metal layer 204 in parallel below the powersupply line Vdd (source metal layer 206) positioned on the side of thelight-emitting portion OLED.

The holding capacitor C is formed by causing an overlapping region tooccur among the plurality of layers (for example, the source metal layer206, gate metal layer 204, and semiconductor layer 202) relating toformation of the holding capacitor C, similarly to the holding capacitorexplained in embodiment 1; near the overlapping region in which theholding capacitor C is formed, the region occupied by the layerpositioned on the lower side among the plurality of layers is formed tobe larger than the region occupied by layers positioned on the upperside. Specifically, as shown in FIG. 11B, if the width of the sourcemetal layer 206 is d11, the width of the gate metal layer 204 is d12,and the width of the semiconductor layer 202 is d13, then the relationd13>d12>d11 obtains. The lower the layer, the larger the pattern shapeis made.

The extent to which the size is increased will depend on the precisionof the manufacturing processes and the pattern density. As one approach,patterns should be formed for each layer such that, when forming layerspositioned on the upper side, even when the maximum possible shift inposition occurs, the region in the layer positioned on the upper sidewill be contained within the region in the layer positioned on the lowerside. In this embodiment also, the differences d13−d12 and d12−d11 aredesigned to be equal to or greater than predicted position shifts inmanufacturing processes.

Holding Capacitor Below the Bank Layer

It is preferable that the above-described holding capacitor be formedbelow the bank layer 208, in order to isolate the above-describedneighboring light-emitting portion. That is, because the bank layer isnecessary for pixel separation, by superposing the wiring region for thepower supply line and the overlapping region for the holding capacitor,the area occupied by the peripheral circuit can be greatly reduced, anda sufficient aperture ratio can be secured.

Reduction of Peripheral Circuit Space

Similarly to embodiment 1, in embodiment 2 a wiring pattern isfabricated such that at least one active element among a plurality oftransistors and other active elements is connected to another activeelement by the same contact hole. Specifically, as shown in FIG. 10, thetransistors T12, T13 and T14 are interconnected by the same contact holeh13. In this way, by designing the circuit such that there are numerouscommon contact points in the circuit, and arranging elements such thatportions which are common contact points are connected by the sameconnection points, the number of contact holes can be reduced, and theoccupied area of the peripheral circuit used for contact holes can bedecreased.

Other features, such as for example the planar shape of thelight-emitting portion, separation from the electrodes of the gate metallayer, peripheral circuit operation, and improvement of the currentmaintenance performance of the peripheral circuit, are similar to thoseof embodiment 1, and an explanation is omitted.

Embodiment 4

FIG. 12 shows a plane view which explains one pixel region and theperipheral wiring pattern for an EL element in embodiment 3 of thisinvention. FIG. 13 shows cross-sectional views which explain the layerstructure at cross-sections indicated in FIG. 12. FIG. 13A and FIG. 13Bshow the layer structure at cross-sections A-A and B-B respectively inFIG. 12. As in embodiment 3, in these drawings the patterns of theprincipal semiconductor layer 202, gate metal layer 204, source metallayer 206, and anode layer 210 can be seen.

Except for the existence of an affinity-controlling film 213 forming astep shape, the configuration of the EL element of embodiment 4 is thesame as the EL element of embodiment 3. Hence the same symbols indrawings are assigned to components which are the same as in embodiment3, and an explanation is omitted.

Features of this embodiment are explained below.

Affinity-Controlling Layer

As shown in FIG. 13B, the light-emitting portion OLED in embodiment 4comprises an affinity-controlling layer 213 between the secondinterlaminar insulating film 207 and the bank layer 208. Thisaffinity-controlling layer 213 need not be formed over the entire pixelregion, but must be provided, at least, near the boundaries of thelight-emitting portion. The affinity-controlling layer 213 must haveaffinity with the liquid material used in forming the light-emittingportion. In this embodiment, the bank layer 208 forms walls near theboundaries of the light-emitting portion; a material which exhibits alack of affinity with the liquid material used when forming thelight-emitting layer 212 or hole injection layer 211 is selected, and isstacked on top of the affinity-controlling layer 213. Consequently theaffinity-controlling layer 213 forms a step shape on the inside of thelight-emitting portion with respect to the wall formed by the banklayer, as shown in FIG. 12 and FIG. 13B.

The material of the affinity-controlling layer 113 is determinedaccording to the properties of the liquid material with which thelight-emitting region is filled using the ink jet method. For example,if the liquid material comprises a liquid such as water which is highlypolar, it is desirable that the affinity-controlling layer have polarbases, at least in the portion making contact with the liquid materialor on the surface. Conversely, if the liquid material comprises anonpolar liquid, it is desirable that the affinity-controlling layerhave nonpolar bases, at least in the portion making contact with theliquid material or on the surface. Also, the extent of the affinity ofthe affinity-controlling layer is determined by the surface tension ofthe liquid material which fills the light-emitting region.

For example, even if a material which chemically has a weak affinity forwater is used as an affinity-controlling layer, if the liquid materialcomprises large quantities of a solvent with a surface tension lowerthan that of water, the surface tension of the liquid material will belower than that of water, and so the affinity-controlling layer willexhibit affinity for the liquid. Hence the type of material to use inthe affinity-controlling layer is changed variously according to theliquid material to be used.

It is preferable that the affinity-controlling layer 213 comprise aninorganic compound or organic compound which in turn comprises one amongAl, Ta or another metal, silicon oxide, silicon nitride, amorphoussilicon, polysilicon, polyimide, an organic compound with fluoridebonds, or a photoresist. If insulating properties are necessary, theaffinity-controlling layer comprises a nonmetallic compound. Theaffinity of these materials is determined by differences in the contactangle with respect to the liquid material. That is, the degree ofaffinity or absence of affinity is determined in relative and notabsolute terms. The degree of affinity can also be adjusted throughsurface treatment methods.

It is preferable that the bank layer 108 comprise a material with weakeraffinity than the affinity-controlling layer 113. This is because, bymaking the affinity of the bank layer weaker than that of theaffinity-controlling layer, the absence of affinity of the bank layercan repel the liquid material to prevent flowing of the liquid materialinto neighboring pixel regions and avoid short-circuits. Also, theabsence of affinity of the bank layer prevents liquid material frombeing drawn excessively toward the bank layer side so that aconcave-shape film is formed.

Thus in this embodiment, an affinity-controlling layer with an affinityfor the liquid material is provided near the boundaries of thelight-emitting portion, so that the uniformity of the thickness of thehole injection layer, light-emitting layer, and other layersconstituting the light-emitting portion can be improved.

According to this embodiment, a bank layer forming a wall near theboundaries of the light-emitting portion exhibits a lack of affinitywith the liquid material, so that short-circuits with the neighboringpixel regions can be prevented.

In this embodiment, the affinity-controlling layer 213 is formed in astep shape; but when the thickness of the layer cross-section can bemade sufficiently great, walls without a step shape, that is, a singlewall without a step with the bank layer, may be formed.

Other advantageous results of embodiment 4 are similar to those ofembodiment 1, and an explanation is omitted.

Embodiment 5

This embodiment relates to a display panel which is an electro-opticaldevice having EL elements which are electro-optical elements explainedin the above embodiments, and electronic device comprising such adisplay panel.

FIG. 14 shows a connection diagram for a display panel 1 of thisembodiment. As indicated in FIG. 1, in display panel 1, pixel regionsare arranged in the display region 11. As pixel regions, the pixelregions 10 of embodiment 1 or embodiment 2, or the pixel regions 20 ofembodiments 3 or 4 may be employed. Control signals are supplied to eachpixel region from the driver region 14, via the light-emission controllines Vgp and write-control lines Vsel. Data signals and a power supplyvoltage are supplied to each pixel region from the driver region 15, viadata lines Idata and power supply lines Vdd.

The display panel 1 of this embodiment can be employed in variouselectronic device. FIG. 15 shows examples of electronic device which canemploy the display panel 1.

FIG. 15A is an example of application to a portable telephone set; theportable telephone 30 comprises an antenna portion 31, voice outputportion 32, voice input portion 33, operation portion 34, and a displaypanel 1 of this invention. Thus a display panel of this invention can beutilized as the display portion.

FIG. 15B is an example of application to a camcorder; the camcorder 40comprises an imaging portion 41, operation portion 42, audio inputportion 43, and a display panel 1 of this invention. Thus a displaypanel of this invention can be utilized as a viewfinder or displayportion.

FIG. 15C is an example of application to a portable personal computer;the computer 50 comprises a camera portion 51, operation portion 52, anda display panel 1 of this invention. Thus a display panel of thisinvention can be utilized as a display portion.

FIG. 15D is an example of application to a head-mounted display; thehead-mounted display 60 comprises a band 61, optical system housingportion 62, and a display panel 1 of this invention. Thus a displaypanel of this invention can be utilized as an image display source.

FIG. 15E is an example of application to a rear projector; the projector70 comprises a housing 71, light source 72, synthetic optical system 73,mirror 74, mirror 75, screen 76, and a display panel 1 of thisinvention. Thus a display panel of this invention can be utilized as animage display source.

FIG. 15F is an example of application to a front projector; theprojector 80 comprises a housing 82, optical system 81, and a displaypanel 1 of this invention, and is capable of displaying images on ascreen 83. Thus a display panel of this invention can be utilized as animage display source.

Electro-optical devices of this invention are not limited to the aboveexamples, but extend to all electronic device to which active-matrixtype display devices can be applied. For example, in addition to theabove, utilization in fax machines with display functions, in theviewfinders of digital cameras, in portable TV sets, in DSP devices, inPDAs, in electronic organizers, in electro-optical bulletin boards, indisplays for advertising and announcements, and in other areas ispossible.

FIG. 1

-   13 CATHODE LEAD ELECTRODE-   12 CATHODE-   1 DISPLAY PANEL-   10 PIXEL REGION-   11 DISPLAY REGION-   14 DRIVER REGION-   15 DRIVER REGION-   16 GLASS SUBSTRATE

FIG. 2

-   SEMICONDUCTOR LAYER-   GATE METAL LAYER-   SOURCE METAL LAYER-   ANODE LAYER

FIG. 8

-   SEMICONDUCTOR LAYER-   GATE METAL LAYER-   SOURCE METAL LAYER-   ANODE LAYER

FIG. 10

-   SEMICONDUCTOR LAYER-   GATE METAL LAYER-   SOURCE METAL LAYER-   ANODE LAYER

FIG. 12

-   SEMICONDUCTOR LAYER-   GATE METAL LAYER-   SOURCE METAL LAYER-   ANODE LAYER

1. An electro-optical device, comprising: an electro-optical element; aholding capacitor that includes a plurality of layers includingelectrodes, the holding capacitor regulating a current supplied to theelectro-optical element; a first transistor that supplies the current tothe electro-optical element according to an electric charge amount heldin the holding capacitor, the first transistor having a first gateelectrode, a first source region and a first drain region; a secondtransistor connected between (i) the first gate electrode and (ii) thefirst source region or the first drain region, the second transistorhaving a second gate electrode; a wiring coupled between the first gateelectrode and the second transistor; a control line that supplies acontrol signal to the second gate electrode, the control line beingdisposed to cross the wiring; a first metal layer that forms a supplyline, the supply line supplying the current to the electro-opticalelement; a second metal layer that forms the first gate electrode; asemiconductor layer that has a first portion, the first portion of thesemiconductor layer forming the first source region and the first drainregion; a first interlaminar insulating film disposed between the firstmetal layer and the second metal layer; and a gate insulating filmdisposed between the second metal layer and the semiconductor layer, theholding capacitor having a first layer, a second layer, and a thirdlayer, the first layer being formed by a portion of the first metallayer, the second layer being formed by a portion of the second metallayer, and the third layer being formed by a second portion of thesemiconductor layer, the second portion of the semiconductor layer beingphysically isolated from the first portion of the semiconductor layer,the first layer being connected to the supply line and forming a firstelectrode of the holding capacitor, the second layer being connected tothe control terminal of the active element and forming a secondelectrode of the holding capacitor, the third layer being electricallyconnected to the first layer via a contact hole so as to form the firstelectrode of the holding capacitor together with the first layer, and afirst width of the first layer positioned on the second layer beingformed to be smaller than a second width of the second layer, and thesecond width of the second layer positioned on the third layer beingformed to be smaller than a third width of the third layer.
 2. Theelectro-optical device according to claim 1, wherein the first layer isa portion of the supply line, and a portion of the second layer formingthe second electrode of the holding capacitor is provided underneath theportion of the supply line forming the first layer and patterned to formthe second electrode.
 3. An electric apparatus comprising theelectro-optical device according to claim
 1. 4. An electro-opticaldevice, according to claim 1, further comprising: a first differencebetween the first width and the second width being designed to be equalto or greater than predicted position shifts between the first layer andthe second layer in their manufacturing processes, and a seconddifference between the second width and the third width being designedto be equal to or greater than predicted position shifts between thesecond layer and the third layer in their manufacturing processes.